Egyptian president Abdel-Fattah El-Sisi said on Sunday that the country will observe three days of mourning following a morning explosion that killed at least 25 people and injured more than 31 at Saint Peter and Saint Paul church near the Coptic Cathedral.
"Terrorism targets the country's and Copts and Muslims... Egypt will only be made stronger and more united in such circumstances," the president said in a statement.
The president vowed to hold accountable the assailants and put on trial all who have "incited, facilitated or participated" in the terrorist attack.
The president described the Sunday church attack – as well as the Friday blast in Giza that left six policemen dead – as part of "a war against the great Egyptian people."
Egypt's Al-Azhar, the world's oldest seat of Sunni Islamic learning, also condemned the attack.
The Anglican Church in Egypt also denounced the attack, saying that "such an attack would not stop people from standing united in the face of terrorism."
The British ambassador in Egypt John Casson said he was "appalled by [the] attack on Coptic Cathedral."
The United Arab Emirates foreign minister Abdallah Bin Zayed, French Minister of Foreign Affairs Jean-Marc Ayrault and the US Embassy in Egypt also condemned the attack.
Egypt has been battling a North Sinai-based Islamist insurgency since the ouster of Islamist president Mohamed Morsi in 2013.
While militant attacks – mostly limited to army and police targets – have mainly been focused in North Sinai, some attacks have reached other parts of the country, including the capital.
Egypt's Christians have been the target of several terrorist attacks in recent years. Several minor attacks targeting churches followed the dispersal of the pro-Morsi Rabaa El-Adaweya sit-in in 2013.
The largest attack targeting Christians in recent years took place in 2011, when 23 people were killed in an explosion at the Two Saints Church in Alexandria.